Coaxial transmission line rf switch

ABSTRACT

A transmission line switch for general use at frequencies to 400 MHz and in certain applications to 1000 MHz, featuring strip-line circuitry. Specifications heretofore met only by more expensive switches are achieved with refined circuit design and improved lead support.

United States Patent 1 1 LeDonne July 31, 1973 COAXIAL TRANSMISSION LINERF 3,471,808 10/1969 Felsenheld et a1 333/7 x SWITCH 3,553,607 1 1971Lehrfeld 333184 M x 3,131,268 4/1964 Omel' 335/5 [75] Inventor: DanielA. LeDonne, New York, N.Y. ,337 12 1963 Wedemeyer,, 333 7 AssigneezPlessey lncotporated, New York 2,842,637 7/1958 Adams et a1 335/4 N.Y.Primary Examiner-Rudolph V. Rolinec Flledi P 24, 1972 AssistantExaminerMarvin Nussbaum Attorney--Louis Mam 61, al.

52 US. (:1 333/7, 333/84 M, 333/97 s [57] ABSTRACT [51] Int. Cl. H011/10, HOlp 3/08 A transmission line switch f g n l e at frequ n- [58]Field of Search 333/7, 13,84 M, cies to 400 MHZ and in certainapplications to 1000 333/97 S; 335/4, 5 MHz, featuring strip-linecircuitry. Specifications heretofore met only by more expensive switchesare 56] Referen e Cit d achieved with refined circuit design andimproved lead support.

9 Claims, 5 Drawing Figures PATENIEB JUL 31 ism sum 2 or 2 COAXIALTRANSMISSION LINE RF SWITCH BACKGROUND OF THE INVENTION The presentinvention relates generally 'to transmission line switches intended foruse in the lower microwave region. More particularly, the inventionrelates to coaxial switches which will meet rigid militaryspecifications but which are more economical to manufacture thanswitches heretofore available, by virtue of employing low-coststrip-line circuitry.

Switches of the type described herein must have the followingcharacteristics:

1. Frequency: DC to 400 MHz.

2. RF Power rating: (non-switching) I watts CW minimum; (switching)watts CW.

3. Impedance: 50 ohms nominal 4. Voltage standing wave ratio (VSWR): 1.3to l (typical).

5. Insertion loss: 0.22 DB maximum (energized and deenergized).

6. Isolation: 33 DB minimum.

7. Operational Life: 10,000 cycles minimum 8. Coil current: 35 MAmaximum I 9. Operating voltage: 18-30 VDC.

10. Environmental requirements: Mil-S-32928B.

l l. Vibration resistance: Mil-S-202C, method 204A, test condition B.

To meet such rigid specifications, it has heretofore been necessary toemploy carfully hand-wired connections to relay terminals, with everyconnection being critical" in terms of length, geometry and strength.

Typical of the prior art devices is the coaxial switch disclosed in U.S.Pat. No. 3,131,268. This switch provides for the input connector to beswitched to either of two output connectors by the action of a push-rodassembly activated by relay. Leaf-spring contacts are attached to theoutput connectors, and the push-rod alternately connects one or theother to the input connector, the unconnected contact being grounded.Leaf spring contacts are, of course, subject to vibration.

The use of strip-line technology in switches of the general typedescribed is not entirely unknown. In U.S. Pat. No. 2,842,637, a relayarmature causes one line conductor to move selectively between a pair ofparallel, spaced line conductors, following the general principle of ajack-type switch, but employing microstrip line conductors withassociated ground conductors. Such a device would not have any degree ofvibration resistance. In U.S. Pat. No. 3,114,887 a U-shaped loop isprinted on a strip-line board which is used as a slider to connect aninput line to either of two output lines. A device of this type wouldhave low vibration resistance and, as with any type of sliding contact,is subject to wear.

As is well known, strip-line technology involves the essentiallyautomatic production of circuitry on a highvolume, low-cost basis. Thestarting material is a circuit board having a layer of copper on eachside. With photolithographic techniques, a positive resist is appliedover the desired circuit pattern, and the remaining, exposed metal isremoved by etching. The resist is then dissolved off, and the copper isplated, generally with nickel and hard gold. Such circuits canbeproduced in volume with precise accuracy and low cost.

Early efforts to adopt strip-line technology to coaxial RF switcheswhich met the exacting requirements noted above were unsuccessful.Vibration tests were failed, resistance was too high, and otherdifficulties were encountered.

OBJECTS OF THE INVENTION A general object of the present invention is toprovide an improved coaxial transmission line RF switch.

A further object of the present invention is to provide a coaxialtransmission line RF switch which meets or exceeds all of theabove-noted requirements, and which is less expensive than switchesheretofore qualitied for the same service.

Another object of the present invention is to provide a coaxialtransmission line RF switch which successfully employs strip-linecircuitry.

Various other objects and advantages of the invention will become clearfrom the following detailed description of embodiments thereof, and thenovel features will be particularly pointed out in connection with theappended claims.

THE DRAWINGS Reference will hereinafter be made to the accompanyingdrawings, wherein:

FIG. 1 is a plan view, partly in section, showing a preferred embodimentof the invention;

FIG. 2 is a cross-sectional elevation taken along line II-Il of FIG. 1;

FIG. 3 is a plan view of a circuit board adapted for installation in theembodiment of FIG. 1 and 2;

FIG. 4 is a schematic diagram of the circuitry of FIG. 3; and

FIG. 5 is a greatly enlarged cross-sectional elevation showing bondingof the center lead to the circuit board.

DESCRIPTION OF EMBODIMENTS In essence, the switch of the presentinvention comprises a rectangular connector body 10 having a soldered-oncover or can 12. Four N-type coaxial connectors 14 are secured to thebody, the center lead 16 of each extending interior of the body andsoldered directly to the printed circuit board 18. The board 18 includescircuitry 20 (described hereinbelow in connection with FIG. 3) and has arelay 22 attached thereon with a mounting clamp 23. A pair of wires 24,26 connect the relay 22 to a pair of insulated terminals 28, 30 mountedin the top of the can 12.

The rectangular box or body 10 is preferably fabricated of silver-platedbrass. The bottom 32 thereof is much thicker than the sides, so thatwhen the PC board 18 is attached thereto with screws 34, its uppersurface will be in contact with the center leads 16 from the fourcoaxial connectors 14. Bottom 32 is tapped at appropriate locations toaccomodate screws 34, and additional holes 36 are drilled to providespace for the relay terminals 38 and the ends of mounting clamp 23.

The sides of box 10 are provided with four identical round holes 40 toaccomodate the connectors 14. As all four connectors are identical, onlyone need be described. The connector body 42 is also preferablyfabricated of silver plated brass, and comprises a threaded cylindercompletely open at one end but having only a small axial opening 44 atthe other end 45. The diameter of body 42 at the end 45 is such that itcan be fitted into opening 40 in box 10 and soldered into place, Anannular shoulder 46 on body 42 keeps the end of body 42 flush with theinterior surface of box 10. A cylindrical insulator 48 fits withinconnector body 42, and is preferably made of a polytetrafluoroethylenematerial such as Teflon (trademark). A projection 50 on the end thereoffills the opening 44. It is noted that projection 50 is deemed essentialfor vibration resistance; it may be a separate insulating member but ispreferably an integral part of insulator 48. Insulator 48 isonly aboutone-half as long as connector body 42, and extends up to an outwardlyextending annular shoulder 52 in body 42. To insure tight frictionengagement between insulator 48 and body 42, the outer surface of theformer may be grooved or roughened. A cylindrical bushing 54 fits withinbody 42 and rests against shoulder 52, thus locking insulator 48 inplace, since the axial opening 56 in bushing 54 has a smaller insidediameter than shoulder 52. Bushing 54 is locked in place by spinningover the end of connector body 42. The inside surface of bushing 54 isslightly tapered so as to snugly engage the male coaxial connector (notshown) when the same is inserted in the connector body. The connector 14is completed with center lead contact 58, which is in serted in andretained by an axial opening 60 in insulator 48. Contact 58 has acontact portion 62, a body portion 64 and a lead 16. The material ofchoice for contact 58 is gold-plated beryllium copper. The contactportion 62 is the end which extends into the cavity defined by bushing54, and comprises an axial opening and four equi-spaced slots. Portion62 is adapted to resiliently receive the center lead of the maleconnector. The body portion 64 is a solid cylinder with the outersurface grooved or notched so as to be frictionally engaged by insulator48 when inserted into opening 60. The lead 16 is connected to orintegral with body portion 64 at the end opposite contact portion 62,and extends through an axial opening in projection 50 into the interiorof box 10.

. The connection and support of lead 16 are important aspects of theinvention, and greatly enlarged detail thereof is shown in FIG. 5. Withreference to that drawing, it is first to be noted that circuit board 18with circuitry 20 is just below and in contact with lead 16. Dimensionsare controlled to obtain an interference fit between leads l6 and thebonding pads on circuitry 20. Next, the extension of lead 16 beyondprojection 50 is as small as possible, i.e., the minimum necessary forsoldering. In practice this is about one-sixteenth inch. The solder 21which connects lead 16 to the circuit 20 extends to substantially theentire exposed length of leqd 16. Thus, between projection 50 and solder21, lead 16 is firmly supported along substantially its entire length.This is important for vibration resistance. Also, if lead 16 is somewhatlarger than other requirements might dictate, vibration resistance isalso improved (0.05 in OD is typical).

The printed circuit board 18 and circuitry 20 will now be described, andattention is directed to FIG. 3. The board 18 is preferably epoxy-bondedfibreglass with copper on each side. The copper on the top side isformed into the circuitry 20 as shown using well known photo-etchingtechniques which need not be described. However, it is important to notethe the circuitry should be as broad as possible consistent withallowable separation. This reduces circuit resistance, im-

proves the impedance match and lowers insertion loss.

In general, the circuitry should be at least about oneeighth inch widewherever possible, which means everywhere except directly beneath thepoints 68 a, b, 0 (shown in dotted lines) where the relay armaturecontacts the board. At these points, the circuitry should match thearmature closely to insure proper operation. Sharp corners in thecircuitry should be avoided, and after the circuit is etched it shouldbe plated with nickel and hard gold (.0002 Ni and .00004 Au aretypical). Additional holes 70 are provided at locations adapted toreceive matching projections on the bottom of relay 22 (other holes arefor screws 34).

FIG. 4 is a schematic diagram of relay 22 and the circuitry of FIG. 3,with contacts 1-4 of FIG. 4 corresponding to bonding pads 1-4 of FIG. 3.Thus, when the switch is not energized the armature of relay 22 coversareas 68a and 68b and current flows along the path 1-4 and 2-3. Whenrelay 22 is energized, the armature pivots and covers area 68c whileopening areas 68a and 68b. Contacts 3 and 4 are open and current flowsin the path 1-2. It will be appreciated that this circuitry is exemplaryonly and other arrangements may be worked out by those skilled in theart.

The preferred relay for use with the invention is the Printact(trademark) relay No. 24 BW2GX12 manufactured by Executone, Inc. anddescribed in US. reissue Pat. No. 24,209. However, other relays adaptedfor PC board mounting and direct armature contact may be employed.

The terminals 28, 30 mounted in the top of can 12 are preferably of thefeed-through capacitor type, such as Allen Bradley FASC 102W. This has acapacitance of lOOOuf and a maximum DC working voltage of 500 volts. Aninductor 72 is attached to one or both terminals within the can (DelevanPart No. 1025-20 is satisfactory). The capacitors and inductor act toreduce cross-talk, a poorly understood phenomena attributable to thewires passing into the cavity. Possible short circuits can be avoided byinstalling thermo-shrink PVC tubing 74 over inductor 72 and itsconnections.

Assembly of the switch is simple and straight forward. The fourconnectors are assembled and soldered into openings 40. It will be notedthat board 18 has four notches, adjacent to and on one side of bondingpads l-4. Board 18 is placed in body 10 with these notches accomodatingthe leads 16. Board 18 is then slid into its proper position, with aninterference fit between the leads l6 and the bonding pads. The leads 16are soldered to the adjacent pads on circuitry 20, care being taken toavoid solder flow except on the pads.

Terminals 28, 30 are soldered to the can 12. Wires 24, 26 are attachedto the terminals 38 on relay 22. One wire is connected to inductor 72,which is connected to terminal 28, and the other wire is connected toterminal 30. The projections on the bottom of relay 22 are inserted inmounting holes 70, and metal clamp 23, which is generally U-shaped withinwardly-extending hooks on the ends, is installed by pressing down overthe relay until the hooks engage the underside of the circuit board 18,through appropriate notches. Assembly is completed by soldering can 12to body 10 at their mating edges.

It will be noted that one side of clamp 23 is close to bonding pad 2,and it has been determined that crosstalk and VSWR properties areimproved if the clamp is notched or made narrower in this area. Further,the possibility of a short circuit with adjacent circuitry will beeliminated if a piece of insulating tubing is placed over this end ofthe clamp.

Soldering of can 12 onto body 10 can create problems of contamination,and it is preferred to leave a small hole in can 12. This helpsdissipate the heat caused by the soldering and allows contaminatinggases to get out of the can prior to sealing of the hole.

Various changes in the details, steps, materials and arrangements ofparts, which have been herein described and illustrated in order toexplain the nature of the invention, may be made by those skilled in theart within the principle and scope of the invention as defined in theappended claims.

What Is Claimed ls:

l. A coaxial high frequency switching device comprising:

a housing;

a plurality of female coaxial connectors adapted to receive male coaxialconnectors mounted exteriorly of said housing in a single plane and eachconnector having a center lead supported by an insulator, the leadextending into said housing a short distance;

a strip-line circuit board having a circuit pattern thereon includingbonding pads at positions coinciding with the positions of said leads,said circuit board being mounted within said housing in the plane ofsaid connectors at a level to effect an interference fit between saidleads and said bonding pads, said leads being bonded to said pads;

a relay secured to said board and having an armature directlycontactable with selected portions of said circuit pattern to effectdesired switching; and insulated terminals in said housing connected tosaid relay.

2. The switching device as claimed in claim 1, wherein'said insulatorsurrounds and supports each said lead through the wall of said housing,and said leads are soldered to said pads along substantially theremainder of their length, whereby said leads are rigidly supportedalong substantially their entire length.

3. The switching device as, claimed in claim 1, wherein said terminalsinclude feed-through capacitors.

4. The switching device as claimed in claim 1,

wherein said circuit board includes notches adjacent to and to one sideof said bonding pads, whereby said board may be inserted over said leadsin said housing and slid into interference fit with said leads.

5. The switching device as claimed in claim 1, wherein said circuitpattern comprises copper plated with nickel and hard gold, and eachconductor therein is at least about one-eighth inch wide whereverpossible.

6. The switching device as claimed in claim 1, wherein said housingcomprises a rectangular body portion having said connectors mounted inwalls thereof and said circuit board mounted on a raised bottom thereof,and a can portion bonded to the walls of said body portion around theperiphery thereof, said can portion having said terminals passingtherethrough.

7. The switching device as claimed in claim 3, wherein an inductor isconnected between one of said capacitors and said relay.

8. The switching device as claimed in claim 4, wherein said relay issecured to said board with clamping means engageable in a pair of saidnotches.

9. In a coaxial high frequency switching device including a plurality ofN-type coaxial connectors secured to a housing, insulated center leadsextending thereinto, and relay means within said housing cooperatingwith circuitry for effecting desired switching between said leads, theimprovements comprising:

a strip-line circuit board having said circuitry on a surface thereofincluding bonding pads in interference fit with and soldered to saidleads;

an insulator securing each said lead within each connector and extendingthrough the wall of said housing, each said lead being supported by saidinsulator or said bonding pad ,and solder along substantially its entirelength;

said relay being secured to said board and having an armature directlycontactable with selected portions of said circuitry to effectv desiredswitching upon energizing or deenergizing said relay.

III

1. A coaxial high frequency switching device comprising: a housing; aplurality of female coaxial connectors adapted to receive male coaxialconnectors mounted exteriorly of said housing in a single plane and eachconnector having a center lead supported by an insulator, the leadextending into said housing a short distance; a strip-line circuit boardhaving a circuit pattern thereon including bonding pads at positionscoinciding with the positions of said leads, said circuit board beingmounted within said housing in the plane of said connectors at a levelto effect an interference fit between said leads and said bonding pads,said leads being bonded to said pads; a relay secured to said board andhaving an armature directly contactable with selected porTions of saidcircuit pattern to effect desired switching; and insulated terminals insaid housing connected to said relay.
 2. The switching device as claimedin claim 1, wherein said insulator surrounds and supports each said leadthrough the wall of said housing, and said leads are soldered to saidpads along substantially the remainder of their length, whereby saidleads are rigidly supported along substantially their entire length. 3.The switching device as claimed in claim 1, wherein said terminalsinclude feed-through capacitors.
 4. The switching device as claimed inclaim 1, wherein said circuit board includes notches adjacent to and toone side of said bonding pads, whereby said board may be inserted oversaid leads in said housing and slid into interference fit with saidleads.
 5. The switching device as claimed in claim 1, wherein saidcircuit pattern comprises copper plated with nickel and hard gold, andeach conductor therein is at least about one-eighth inch wide whereverpossible.
 6. The switching device as claimed in claim 1, wherein saidhousing comprises a rectangular body portion having said connectorsmounted in walls thereof and said circuit board mounted on a raisedbottom thereof, and a can portion bonded to the walls of said bodyportion around the periphery thereof, said can portion having saidterminals passing therethrough.
 7. The switching device as claimed inclaim 3, wherein an inductor is connected between one of said capacitorsand said relay.
 8. The switching device as claimed in claim 4, whereinsaid relay is secured to said board with clamping means engageable in apair of said notches.
 9. In a coaxial high frequency switching deviceincluding a plurality of N-type coaxial connectors secured to a housing,insulated center leads extending thereinto, and relay means within saidhousing cooperating with circuitry for effecting desired switchingbetween said leads, the improvements comprising: a strip-line circuitboard having said circuitry on a surface thereof including bonding padsin interference fit with and soldered to said leads; an insulatorsecuring each said lead within each connector and extending through thewall of said housing, each said lead being supported by said insulatoror said bonding pad and solder along substantially its entire length;said relay being secured to said board and having an armature directlycontactable with selected portions of said circuitry to effect desiredswitching upon energizing or deenergizing said relay.